In order to provide a stable environment for the growth of bacteria in measuring vessels, such as flasks or test tubes or cultivation tubes, either thermal chambers or thermoblocks are generally employed. Thermal chambers generally have areas all around the samples or vessels or at least over a substantial portion of the peripheries thereof which are not obstructed to allow viewing of the interiors of the vessels and, in addition to observation, analysis of the contents of the vessels. Thermoblocks, by contrast, have compartments closely receiving the vessels with the walls of the compartments practically hugging the walls of the vessels to maximize thermal conductivity between the block and each vessel. While the latter ensures an effective thermal equilibrium between the block and the interior of the vessel, it has the drawback that the vessel walls are not accessible for manipulation or measurement, the ability to observe the contents of the vessel is restricted and the system has a very high mass.
Measurements of bacterial growth can be effected electrically via the impedance measurement of the contents of the vessel between two or more electrodes. Alternatively, the cloudiness or degree of turbidity can be determined and radiation, utilizing the visible light spectrum or invisible waves, can be utilized. It is also possible to employ electrical or magnetic fields or radioactive media to monitor the bacterial culture. The display or registering of the parameters of bacterial cultures can be effected automatically during a particular observation period and the culturing process can be programmed or controlled automatically.
Notwithstanding the fact that prior art thermal chambers and thermoblocks have been found to be highly effective in achieving temperature equilibration among the samples and between the samples and the heating and cooling units of the apparatus, in practically all of the earlier devices the compromises between accessibility to the sample vessel and the need for close proximity of the sample vessel to a wall of the thermally modulated structure have led to unacceptable results.